First check
Try one simple request that does not depend on a third-party skill, then check the Echo connection in the Alexa app.
What to do
If the Echo is offline or requests time out, restart the supported power source and the home network only if other devices also show connectivity trouble. Wait for the Echo to reconnect before testing again.
Done when
A built-in Alexa request completes normally and the app shows the Echo online.
If it still fails
If the Echo is online but built-in requests still fail, check Amazon/Alexa service status and the device support flow. Reserve a factory reset for the model-specific support path.